Resonant devices, such as resonant vibratory devices and sensors, have long served various technical functions in many important industries. For example, in past decades resonant devices such as oscillators, vibratory sensors, gyroscopes and vibratory accelerometers, have been adapted in military and transportation applications.
In recent years, however, the demands of such industries have shifted or increased, and, in turn, characteristics and/or performance levels of resonant devices that were previously accepted as satisfactory have become unsuitable. For example, inertial technology in various industries had long relied upon inertial measurement units (IMUs) that employed fiber optic gyroscopes (FOGs) or ring laser gyroscopes (RLGs). Over time, it became clear that such devices tended to be disadvantageously large and power consumptive and/or suffered from issues relating to dead-band non-linearities and/or light source life. The large size/volume of such devices became a particular problem, since industries in which they were being used, especially the military and transportation industries, were increasingly seeking to incorporate such devices in miniature and/or portable platforms.
This led those in the art to begin developing Micro-Electro-Mechanical System (or “MEMS”)-based resonant devices, such as MEMS-based gyroscopes. MEMS-based resonant devices offered several critical advantages (e.g., small volume and mass, low power usage, reduced cost through batch fabrication), which led to them being adopted on a widespread scale in various cutting edge technologies, such as in military sensors and weapons.
In the fabrication of such devices, for example the Disc Resonator Gyro (or Disc Resonator Gyroscope, or “DRG”), sophisticated fabrication methods are used. One approach to fabricating DRGs is to use substantially conventional MEMS processing methods, in which structures exhibiting extremely precise geometrical definition and relationships can be produced. In fabrication of DRGs using these conventional methods, it has been the usual procedure to process two sections of the device on separate wafers, such as silicon wafers, and then to precisely align the two sections prior to bonding the two sections together to produce a complete DRG device. The conventional process requires alignment at a precision that is at or beyond the limits of conventional mechanical alignment techniques, considering in particular that alignment in three degrees of freedom (e.g., length, width, and angular orientation) is required to completely align two wafers having MEMS structures defined therein. The problems associated with the alignment step have proven to be severe and they can severely and negatively impact device yield and thereby device cost and availability.
There is a need for fabrication methods that allow the convenient fabrication of DRG devices in higher yields.